Electrochemical tuning and mechanical resilience of single wall carbon nanotubes

Single-wall carbon nanotubes (SWNTs) are fascinating systems exhibiting many novel physical properties. In this paper, we give a brief review of the structural, electronic, vibrational, and mechanical properties of carbon nanotubes. In situ resonance Raman scattering of SWNTs investigated under electrochemical biasing demonstrates that the intensity of the radial breathing mode varies significantly in a nonmonotonic manner as a function of the cathodic bias voltage, but does not change appreciably under anodic bias. These results can be quantitatively understood in terms of the changes in the energy gaps between the 1D van Hove singularities in the electron density of states, arising possibly due to the alterations in the overlap integral of π bonds between the p-orbitals of the adjacent carbon atoms. In the second part of this paper, we review our high-pressure X-ray diffraction results, which show that the triangular lattice of the carbon nanotube bundles continues to persist up to ~10 GPa. The lattice is seen to relax just before the phase transformation, which is observed at ~10 GPa. Further, our results display the reversibility of the 2D lattice symmetry even after compression up to 13 GPa well beyond the 5 GPa value observed recently. These experimental results explicitly validate the predicted remarkable mechanical resilience of the nanotubes

Single-Walled Carbon Nanotube Bundles Intercalated with Semiconductor Nanoparticles

Nanoparticles of CdSe, CdS and ZnSe have been incorporated in the inter-tubular gaps of single-walled carbon nanotube (SWNT) bundles. Electron microscope, X-ray diffraction (XRD), electronic spectroscopy and Raman studies have been employed to characterize these systems. The lengths of the intercalate inside the bundles could be varied by changing the reaction conditions. Electronic absorption and photoluminescence studies from the semiconductor intercalates show the expected blue-shift with respect to the corresponding bulk samples in CdS and ZnS samples. The SWNT lattice is expanded on incorporating CdSe as confirmed by XRD in the low-angle range. The expansion in the lattice is also corroborated by the Raman measurements which show a considerable red-shift for both the radial and the tangential modes of the SWNT signal, thus signifying an increase in the van der Waals gap between the tubes in the bundle. The red-shift of the Raman signal is due to the decrease in the inter-tube interactions as well as due to doping effects

Pressure-induced phase transformation and structural resilience of single-wall carbon nanotube bundles

We report here an in situ X-ray diffraction investigation of the structural changes in carbon single-wall nanotube bundles under quasihydrostatic pressures up to 13 GPa. In contrast with a recent study [Phys. Rev. Lett. 85, 1887 (2000)] our results show that the triangular lattice of the carbon nanotube bundles continues to persist up to ~10 GPa. The lattice is seen to relax just before the phase transformation that is observed at ~10 GPa. Further, our results display the reversibility of the two-dimensional lattice symmetry even after compression up to 13 GPa well beyond the 5 GPa value observed recently. These experimental results explicitly validate the predicted remarkable mechanical resilience of the nanotubes

Single-walled carbon nanotube bundles intercalated with semiconductor nanoparticles

Nanoparticles of CdSe, CdS and ZnSe have been incorporated in the inter-tubular gaps of single-walled carbon nanotube (SWNT) bundles. Electron microscope, X-ray diffraction (XRD), electronic spectroscopy and Raman studies have been employed to characterize these systems. The lengths of the intercalate inside the bundles could be varied by changing the reaction conditions. Electronic absorption and photoluminescence studies from the semiconductor intercalates show the expected blue-shift with respect to the corresponding bulk samples in CdS and ZnS samples. The SWNT lattice is expanded on incorporating CdSe as confirmed by XRD in the low-angle range. The expansion in the lattice is also corroborated by the Raman measurements which show a considerable red-shift for both the radial and the tangential modes of the SWNT signal, thus signifying an increase in the van der Waals gap between the tubes in the bundle. The red-shift of the Raman signal is due to the decrease in the inter-tube interactions as well as due to doping effects

A Raman study of CdSe and ZnSe nanostructures

Raman studies have been carried out on CdSe nanotubes and ZnSe nanorods produced by surfactant-assisted synthesis. The Raman spectrum of CdSe nanotubes shows modes at 207.5 and 198 cm(-1); the former arises from the longitudinal optic phonon mode red-shifted with respect to the bulk mode because of phonon confinement, and the latter is the I = 1 surface phonon. Analysis based on the phonon confinement model demonstrates that the size of the nanoparticle responsible for the red-shift is about 4 nm, close to the estimate from the blue-shift of the photoluminescence. The Raman spectrum of ZnSe,nanorods shows modes at 257 and 213 cm(-1), assigned to longitudinal and transverse optic phonons, blue-shifted with respect to the bulk ZnSe modes because of compressive strain. The mode at 237 cm(-1) is the surface phonon

Pressure-induced reversible transformation in single-wall carbon nanotube bundles studied by Raman spectroscopy

We report our high-pressure Raman studies on single-wall carbon nanotube bundles carried out up to 25.9 GPa. The intensity of the radial modes decreases more drastically as compared to that of the tangential modes. The former could be followed up in pressure runs to 3 GPa. The most intriguing observation is the anomalous pressure behaviour of the 1594 cm(-1) tangential mode between 10 and 16 GPa. This feature, as well as the pressure dependence of intensity, peak position and linewidth, are reversible on decompression. The anomalous pressure dependence is argued to be associated with faceting of the tubes in the bundle, showing their remarkable resilience

Single-walled carbon nanotube bundles intercalated with semiconductor nanoparticles

Nanoparticles of CdSe, CdS and ZnSe have been incorporated in the inter-tubular gaps of single-walled carbon nanotube (SWNT) bundles. Electron microscope, X-ray diffraction (XRD), electronic spectroscopy and Raman studies have been employed to characterize these systems. The lengths of the intercalate inside the bundles could be varied by changing the reaction conditions. Electronic absorption and photoluminescence studies from the semiconductor intercalates show the expected blue-shift with respect to the corresponding bulk samples in CdS and ZnS samples. The SWNT lattice is expanded on incorporating CdSe as confirmed by XRD in the low-angle range. The expansion in the lattice is also corroborated by the Raman measurements which show a considerable red-shift for both the radial and the tangential modes of the SWNT signal, thus signifying an increase in the van der Waals gap between the tubes in the bundle. The redshift of the Raman signal is due to the decrease in the inter-tube interactions as well as due to doping effects

Pressure-induced reversible transformation in single-wall carbon nanotube bundles studied by Raman spectroscopy

Abstract We report our high-pressure Raman studies on single-wall carbon nanotube bundles carried out up to 25.9 GPa. The intensity of the radial modes decreases more drastically as compared to that of the tangential modes. The former could be followed up in pressure runs to 3 GPa. The most intriguing observation is the anomalous pressure behaviour of the 1594 cm y1 tangential mode between 10 and 16 GPa. This feature, as well as the pressure dependence of intensity, peak position and linewidth, are reversible on decompression. The anomalous pressure dependence is argued to be associated with faceting of the tubes in the bundle, showing their remarkable resilience.

Pressure-induced reversible transformation in single-wall carbon nanotube bundles studied by Raman spectroscopy

We report our high-pressure Raman studies on single-wall carbon nanotube bundles carried out up to 25.9 GPa. The intensity of the radial modes decreases more drastically as compared to that of the tangential modes. The former could be followed up in pressure runs to 3 GPa. The most intriguing observation is the anomalous pressure behaviour of the 1594 cm−1 tangential mode between 10 and 16 GPa. This feature, as well as the pressure dependence of intensity, peak position and linewidth, are reversible on decompression. The anomalous pressure dependence is argued to be associated with faceting of the tubes in the bundle, showing their remarkable resilience

Pressure-induced phase transformation and structural resilience of single-wall carbon nanotube bundles

We report here an in situ x-ray diffraction investigation of the structural changes in carbon single-wall nanotube bundles under quasihydrostatic pressures up to 13 GPa. In contrast with a recent study [Phys. Rev. Lett. 85, 1887 (2000)] our results show that the triangular lattice of the carbon nanotube bundles continues to persist up to ~10 GPa. The lattice is seen to relax just before the phase transformation that is observed at ~10 GPa. Further, our results display the reversibility of the two-dimensional lattice symmetry even after compression up to 13 GPa well beyond the 5 GPa value observed recently. These experimental results explicitly validate the predicted remarkable mechanical resilience of the nanotubes